1. Field of the Invention
The present invention relates generally to a method of feedback controlling idle speed of an internal combustion engine to a target speed, and more specifically to a method of feedback controlling engine idle speed on the basis of engine state variables estimated in accordance with mathematical dynamic models, in which an engine is managed as a dynamic system under the consideration of engine internal states and the engine dynamic behavior is estimated on the basis of mathematical dynamic models of state variables representative of engine internal states in order to determine engine idle speed controlling values. The above-mentioned state variable feedback control method is quite different from the conventional proportional, integral or differential feedback control method.
2. Description of the Prior Art
Various engine idle speed control systems for internal combustion engines are well known. In these systems, when the engine is determined to be idled in response to a signal outputted from a throttle valve idle switch, a neutral signal from a transmission neutral switch, a vehicle speed signal from a speed sensor, etc., a basic target engine idle speed is calculated according to coolant temperature detected by a coolant temperature sensor on the basis of table look-up method and then corrected to a final target engine idle speed under the consideration of the on-off state of an air conditioning system and the magnitude of battery voltage. Thereafter, the quantity of air bypassing the throttle value, for instance, is so adjusted by proportional or integral feedback control method that the difference in engine idle speed between the calculated and corrected target value and the actually detected value is minimized.
In the conventional engine idle speed control systems, however, there exists a problem in that the response speed of the control system is not sufficient, in particular, in the transient state where engine torque is disturbed due to neutral-to-drive shifting of the transmission lever or vice-versa, air conditioning system cycling or power steering pump connection or disconnection to or from the engine. This is because a proportional or integral feedback control system does not agree with the system in which a plurality of signals are feedbacked thereto.
A more detailed description of an example of a prior-art engine idle speed control system of this type will be made with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.
Further, recently, some methods of feedback controlling engine idle speed have been proposed on the basis of mathematical dynamic models to determine state variables representative of engine dynamic behavior. However, in these methods, since the order of the mathematical dynamic models is relatively high, the resulting controlling calculations are complicated, thus giving rise to a complicated control system and a higher manufacturing cost.